System and method for detecting a location of fault in a cable

ABSTRACT

The present invention is related to a system and a method for detecting a location of fault in a cable. The system for detecting a location of fault in a cable in accordance with an embodiment of the present invention includes: a cable, transmitting a fault current; a current transforming unit, connected to the cable and receiving the fault current and detecting an original signal of fault current; a detecting unit, detecting a first detail signal and a second detail signal from the original signal of fault current, the first detail signal and second detail signal being detail components in a high frequency band; a comparing unit, comparing the first detail signal with a preset reference value and determining a fault in the cable; and a signal filtering unit, generating a first filtering signal and a second filtering signal by use of the first detail signal and the second detail signal and outputting a fault detection signal based on a result of comparing the first detail signal with the second filtering signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application Nos.10-2009-0093331 and 10-2010-0045961, filed with the Korean IntellectualProperty Office on Sep. 30, 2009 and May 17, 2010, respectively, thedisclosure of which is incorporated herein by reference in theirentirety.

BACKGROUND

1. Technical Field

The present invention is related to a system and a method for detectinga location of fault in a cable.

2. Description of the Related Art

In order to detect the location of fault in an underground cable usedfor extra high voltage transmission, various methods, such as the Murrayloop method using Wheatstone bridge principles, a method using TDR (TimeDomain Reflectometer) based on the principle of progressive wave and thepin pointing method, are used. These methods are applied in an off-lineenvironment to detect the location of fault in an underground cable.When fault occurs, the relevant line needs to be completely separatedfrom the system for the detection of the location of fault, therebytaking a great amount of time to detect the location of fault and torepair the fault.

SUMMARY

The present invention provides a system for detecting a location offault in a cable that can perform an on-line detection of the locationof fault.

The present invention also provides a method of detecting a location offault in a cable that can perform an on-line detection of the locationof fault using the system for detecting a location of fault in a cable.

An aspect of the present invention features a system for detecting alocation of fault in a cable.

The system for detecting a location of fault in a cable in accordancewith an embodiment of the present invention can include: a cable,transmitting a fault current; a current transforming unit, connected tothe cable and receiving the fault current and detecting an originalsignal of fault current; a detecting unit, detecting a first detailsignal and a second detail signal from the original signal of faultcurrent, the first detail signal and second detail signal being detailcomponents in a high frequency band; a comparing unit, comparing thefirst detail signal with a preset reference value and determining afault in the cable; and a signal filtering unit, generating a firstfiltering signal and a second filtering signal by use of the firstdetail signal and the second detail signal and outputting a faultdetection signal based on a result of comparing the first detail signalwith the second filtering signal.

Another aspect of the present invention features a method of detecting alocation of fault in a cable.

The method of detecting a location of fault in a cable in accordancewith an embodiment of the present invention can include: extracting anoriginal signal of fault current at either end of the cable; detecting afirst approximation signal and a first detail signal from the originalsignal of fault current through wavelet transform; determining whetheror not a fault is occurred in the cable by comparing the first detailsignal with a preset reference value; detecting a second approximationsignal and a second detail signal from the first approximation signalthrough wavelet transform; generating a first filtering signal bycomputing the first detail signal and the second detail signal;generating a second filtering signal with a correlation equation that isset by using the first detail signal and the first filtering signal; andoutputting a fault detection signal by comparing the first detail signalwith the second filtering signal.

Yet another aspect of the present invention features a recording mediumhaving recorded a program for realizing a method of detecting a locationof fault in a cable.

The recording medium having recorded the program for realizing themethod of detecting a location of fault in a cable in accordance with anembodiment of the present invention can be read by an electronic device,and the method of detecting a location of fault in a cable can include:extracting an original signal of fault current at either end of thecable; detecting a first approximation signal and a first detail signalfrom the original signal of fault current through wavelet transform;determining whether or not a fault is occurred in the cable by comparingthe first detail signal with a preset reference value; detecting asecond approximation signal and a second detail signal from the firstapproximation signal through wavelet transform; generating a firstfiltering signal by computing the first detail signal and the seconddetail signal; generating a second filtering signal with a correlationequation that is set by using the first detail signal and the firstfiltering signal; and outputting a fault detection signal by comparingthe first detail signal with the second filtering signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system for detecting a location of fault in a cablein accordance with an embodiment of the present invention.

FIG. 2 illustrates wavelet conversion of a detecting unit in accordancewith an embodiment of the present invention.

FIG. 3 is a graph for illustrating a reference value that is set in acomparing unit in accordance with an embodiment of the presentinvention.

FIG. 4 illustrates a method of detecting a location of fault in a cablein accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Since there can be a variety of permutations and embodiments of thepresent invention, certain embodiments will be illustrated and describedwith reference to the accompanying drawings. This, however, is by nomeans to restrict the present invention to certain embodiments, andshall be construed as including all permutations, equivalents andsubstitutes covered by the ideas and scope of the present invention.

Terms such as “first” and “second” can be used in describing variouselements, but the above elements shall not be restricted to the aboveterms. The above terms are used only to distinguish one element from theother. For instance, the first element can be named the second element,and vice versa, without departing the scope of claims of the presentinvention. The term “and/or” shall include the combination of aplurality of listed items or any of the plurality of listed items.

When one element is described as being “connected” or “accessed” toanother element, it shall be construed as being connected or accessed tothe other element directly but also as possibly having another elementin between. On the other hand, if one element is described as being“directly connected” or “directly accessed” to another element, it shallbe construed that there is no other element in between.

Hereinafter, some embodiments of the present invention will be describedin detail with reference to the accompanying drawings. Identical orcorresponding elements will be given the same reference numerals,regardless of the figure number, and any redundant description of theidentical or corresponding elements will not be repeated. Throughout thedescription of the present invention, when describing a certaintechnology is determined to evade the point of the present invention,the pertinent detailed description will be omitted.

FIG. 1 is a diagram illustrating a system for detecting a location offault in a cable in accordance with an embodiment of the presentinvention.

Referring to FIG. 1, a system for detecting a location of fault in acable 100 includes a cable 110, first and second current transformingunits 121, 123, first and second detecting units 131, 133, first andsecond comparing units 141, 143, first and second signal filtering units151, 153 and a computing unit 160.

The cable 110 transmits an electrical current.

The first and second current transforming units 121, 123 are arranged bybeing connected to either end of the cable 110. The first and secondcurrent transforming units 121, 123 are located at end parts of thecable 110 to receive a fault current from the cable 110. The first andsecond current transforming units 121, 123 detect an original signal offault current from the fault current. The first and second currenttransforming units 121, 123 provide the detected original signal offault current to the first and second detecting units 131, 133.

The first and second detecting units 131, 133 receive the originalsignal of fault current. The first and second detecting units 131, 133apply wavelet transform to the original signal of fault current. Afterthe application of the wavelet transform, the first and second detectingunits 131, 133 detect a first approximation signal, which is in a lowfrequency band, and a first detail signal, which is in a high frequencyband, from the original signal of fault current. The first and seconddetecting units 131, 133 provide the first detail signal to the firstand second comparing units 141, 143.

In an example, the first and second detecting units 131, 133 can applythe wavelet transform to the original signal of fault current by use ofMATLAB by The MathWorks, Inc.

Here, the wavelet transform is a part of analytics that is used inrelations to signal processing, video processing, etc. The wavelettransform is appropriate for detecting the location of fault becauseanalysis of an excessive signal is possible not only in a frequency bandbut also in a time domain. The wavelet transform sets the waveform of awavelength as its basic waveform and verifies a correlation by changingits size and location. The wavelet transform changes the size in asimilar concept as the frequency change of Fourier series. Since thewavelet transform changes the location of the waveform of a wavelengthtogether with the size, it is possible to find time information. Forexample, since the wavelet transform shows variable windowcharacteristics in a time-scale domain, high-frequency components areshown in a low scale, and low-frequency components are shown in a highscale.

Hereinafter, the wavelet transform of the first and second detectingunits 131, 133 will be described with reference to FIG. 2, whichillustrates wavelet conversion of a detecting unit in accordance with anembodiment of the present invention. Here, for the convenience ofdescription, the first detecting unit 131 will be used for thedescription.

Referring to FIG. 2 further, the first detecting unit 131 includes firstto n^(th) wavelet filtering units 131-1, 131-2, . . . , 131-n. The firstwavelet filtering unit 131-1 allows an original signal of fault current,which is represented as “S” in FIG. 2, to pass through a low pass filterand a high pass filter to extract a first approximation signal, which isrepresented as “A1” in FIG. 2, in a low frequency band and a firstdetail signal, which is represented as “D1” in FIG. 2, in a highfrequency band from the original signal of fault current S. The secondwavelet filtering unit 131-2 extracts a second approximation signal A2in a low frequency band and a second detail signal D2 in a highfrequency band from the first approximation signal A1. The firstdetecting unit 131 continues the extracting steps using the first ton^(th) wavelet filtering units 131-1, 131-2, . . . , 131-n until adesired signal is obtained from the original signal of fault current S.

Referring to FIG. 1 again, the first and second comparing units 141, 143receive the first detail signal from the first and second detectingunits 131, 133. The first and second comparing units 141, 143 comparethe first detail signal with a preset reference value. Here, thereference value is set as a reference for determining a fault in thecable 110. A fault in the cable 110 can have different characteristicsdepending on the state, load conditions or fault resistance of the cable110. Accordingly, the reference value can be set variously according tothe state or conditions of the cable 110.

Here, the reference value will be described further with reference toFIG. 3.

FIG. 3 is a graph for illustrating a reference value that is set in acomparing unit in accordance with an embodiment of the presentinvention.

Referring to FIG. 3 further, the first and second comparing units 141,143 compare the first detail signal with a reference value 190 setaccording to the state or conditions of the cable 110. In an example,the reference value 190 can be set as a sampling point of 8350.

The first and second comparing units 141, 143 determine that the cable110 is in a fault state if the first detail signal exceeds the referencevalue 190. The first and second comparing units 141, 143 determine thatthe cable 110 is in a normal state if the first detail signal is belowor equal to the reference value 190. If the first detail signal exceedsthe reference value 190, the first and second comparing units 141, 143notify the first and second detecting units 131, 133 of the occurrenceof fault.

Referring to FIG. 1 again, the first and second detecting units 131, 133apply the wavelet transform to the first approximation signal if a faultis occurred in the cable 110. The first and second detecting units 131,133 detect the second approximation signal and the second detail signalfrom the first approximation signal. Since this has been described abovewith reference to FIG. 2, detailed description will be omitted. Thefirst and second detecting units 131, 133 provide the first detailsignal or the second detail signal to the first and second signalfiltering units 151, 153.

The first and second signal filtering units 151, 153 receive the firstdetail signal and the second detail signal from the first and seconddetecting units 131, 133. The first and second signal filtering units151, 153 make a computation in accordance with a correlation of thefirst detail signal and the second detail signal.

Specifically, the first and second signal filtering units 151, 153generate a first filtering signal using a multi-scale correlation methodbased on the correlation of the first detail signal and the seconddetail signal. For example, the first and second signal filtering units151, 153 generate the first filtering signal by multiplying the firstdetail signal by the second detail signal.

In addition, the first and second signal filtering units 151, 153generate a second filtering signal by computing the first detail signaland the first filtering signal.

The second filtering signal can be generated by the followingcorrelation equation.

$\begin{matrix}{{C\_ new} = {C \times \sqrt{\frac{\sum D_{1}^{2}}{\sum C^{2}} \times 2}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, C is the first filtering signal, C_new is the second filteringsignal, and D₁ is the first detail signal.

The correlation equation is set to multiply a correlation coefficient,which uses a summed value obtained by squaring a value of the firstdetail signal and a summed value obtained by squaring a value of thefirst filtering signal, by the first filtering signal.

As the second detail signal is applied with the wavelet transform, noiseincluded in a signal exceeding the first detail signal is reduced. Atthe same time, in the second detail signal, a reflected wave, which hasa more regular pattern in proportion to the length of the cable 110 thanan irregularly occurred noise does, shows a peak in the same timedomain. In other words, the number of maxima in which noise is includedis gradually reduced as the scale increases. Therefore, multiplying thefirst detail signal by the second detail signal further increases thedifference between the peak value and the noise.

Here, in order to detect a more complete correlation signal from thefirst filtering signal, the second filtering signal is generated bymultiplying the first filtering signal by the coefficient of

$\sqrt{\frac{\sum D_{1}^{2}}{\sum C^{2}} \times 2}.$

Since the first filtering signal, which is generated by multiplying thefirst detail signal by the second detail signal, becomes bigger than thefirst detail signal, the first detail signal is doubled, and then thesecond filtering signal is generated by taking a coefficient that is asquare root of the sum of squares of the first detail signal divided bythe sum of squares of the first filtering signal. For example, in orderto reflect each of the first detail signal and the first filteringsignal in the coefficient in Equation 1, the squares of each signal aresummed and applied in Equation 1. The sum of the squares of the firstdetail signal and the sum of the squares of the first filtering signalare configured to include a number of signal components in order toreflect the signal components of each of the first detail signal and thefirst filtering signal.

The first and second signal filtering units 151, 153 compare an absolutevalue of the first detail signal with an absolute value of the seconddetail filtering signal. Here, the second filtering signal can have agreater absolute value than the first detail signal, in case a faultoccurs in the cable 110. The second filtering signal is greater than thefirst detail signal because the fault current detected when the faultcurrent is reflected at a first end part 111 and a second end part 113has an increased noise when the fault occurs.

Alternatively, the second filtering signal can have a smaller absolutevalue than the first detail signal because the noise component of thesecond filtering signal is reduced when the scale is increased.

If the absolute value of the second filtering signal is greater than theabsolute value of the first detail signal, the first and second signalfiltering units 151, 153 determine that the second filtering signal is areflected wave reflected by the cable 110, after which the first andsecond signal filtering units 151, 153 output the second filteringsignal as a fault detection signal.

If the absolute value of the second filtering signal is smaller than orequal to the first detail signal, the first and second signal filteringunits 151, 153 determine that the second filtering signal is a noise andremove the second filtering signal. After the removal, the first andsecond signal filtering units 151, 153 output the first detail signal asthe fault detection signal.

If the value obtained by multiplying the first filtering signal by thecoefficient is greater than the first detail signal, the first andsecond signal filtering units 151, 153 determine that the secondfiltering signal is a reflected wave, output the first filtering signalas the fault detection signal, and treat and remove other signals asnoise.

The computing unit 160 is connected with the first and second signalfiltering units 151, 153 to receive the fault detection signal. Here,the computing unit 160 is connected with the first and second signalfiltering units 151, 153 by use of a data communication device 170. Forexample, the computing unit 160 computes a delay time of the faultdetection signal by using the data communication device 170 thatutilizes a communication line including an optical cable or a GPSapparatus.

The computing unit 160 computes the distance to a location of fault byuse of the delay time of the fault detection signal and the transmissionspeed of the cable 110. The computing unit 160 computes the distance tothe location of fault by using the following equation.

$\begin{matrix}{X = \frac{L + {v \cdot \left( {{TA}_{p\; 1} - {TB}_{p\; 1}} \right)}}{2}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, “X” is the distance to the location of fault, and “L” is adistance between both ends of the cable, while “v” is the transmissionspeed of the cable, “TA_(P1)” a first arrival time of a first signalarriving at the first end part 111, “TB_(P1)” a second arrival time of afirst signal arriving at the second end part 113.

The computing unit 160 receives the delay time, which is the differencein arrival time of progressive waves, each of which arrives at the firstend part 111 and the second end part 113. The computing unit 160multiplies the delay time by the transmission speed of the cable 110 andthen adds the distance between both ends of the cable 110 to themultiplied value before dividing into two.

For example, if it is assumed that a fault has occurred at a locationthat is 20 km away from one end of the cable 110, the first detailsignal, from which noise is removed through the first and second signalfiltering units 151, 153, arrives at either end of the cable 110 in thefirst arrival time of TA_(p1) and the second arrival time of TB_(p1),respectively. Here, if it is set that the distance L between both endsof the cable 110 is 101.7 km, the transmission speed v of the cable 110is approximately 137.2 m/μs, the first arrival time TA_(p1) is 0.008475,and the second arrival time TB_(p1) is 0.008924, the computing unit 160can compute that the distance to the location of fault is approximately20.24 km.

The system for detecting a location of fault in a cable in accordancewith an embodiment of the present invention detects the location offault in the cable by generating the first filtering signal using thefirst detail signal and the second detail signal that are obtainedthrough wavelet transform, removing the noise by comparing the firstdetail signal with the second filtering signal that is generated usingthe first filtering signal and the first detail signal, and outputtingthe signal determined to be the reflected wave. Accordingly, the systemfor detecting a location of fault in a cable in accordance with anembodiment of the present invention can make an on-line detection of thefault location in the cable.

In the system for detecting a location of fault in a cable in accordancewith an embodiment of the present invention, the signal filters caneffectively remove a great amount of noise included in the originalsignal of fault current and detect the signals reflected by the cableonly, thereby reducing the effect of rapid signal attenuation.Therefore, the system for detecting a location of fault in a cable inaccordance with an embodiment of the present invention can detect thelocation of fault accurately.

FIG. 4 illustrates a method of detecting a location of fault in a cablein accordance with an embodiment of the present invention. Hereinafter,the method of detecting a location of fault in a cable will be describedwith reference to the system for detecting a location of fault in acable illustrated in FIG. 1.

Referring to FIG. 4, the method of detecting a location of fault in acable in accordance with an embodiment of the present inventionincludes: extracting an original signal of fault current (S10);detecting a first detail signal (S20); comparing the first detail signalwith a reference value (S30); detecting a second filtering signal (S40);generating a first filtering signal (S50); generating a second filteringsignal (S60); detecting a fault detection signal by comparing the firstdetail signal with the second filtering signal (S70); and detecting thelocation of fault (S80).

In the step of S10, current transforming units are arranged at eitherend of a current-transmitting cable and extract an original signal offault current. Here, the current transforming units receive the faultcurrent from the cable and extract the original signal of fault currentthrough data sampling.

In the step of S20, detecting units apply wavelet transform to theoriginal signal of fault current and detect a first approximationsignal, which is in a low frequency band, and a first detail signal,which is in a high frequency band.

In the step of S30, comparing units receive the first detail signal fromthe detecting units and compare the first detail signal with a presetreference value. Here, the reference value is set as a reference fordetermining a fault in the cable. Since the fault in the cable can havedifferent characteristics depending on the state, load conditions orfault resistance of the cable, the reference value can be set variouslyaccording to the state or conditions of the cable.

The comparing units compare the first detail signal with the referencevalue to determine whether or not there is a fault in the cable. Thecomparing units determine that there is no fault occurred in the cableif the first detail signal is below or equal to the reference value. Ifthe first detail signal exceeds the reference value, the comparing unitsdetermine that a fault is occurred in the cable.

In the step of S40, the detecting units apply the wavelet transform tothe first approximation signal if a fault is determined to have occurredin the cable according to the result of comparison by the comparingunits, and detect a second approximation signal and a second detailsignal. Here, the second approximation signal is an approximationcomponent in a low frequency band that is detected from the firstapproximation signal. The second detail signal is a detail component ina high frequency band that is detected from the first approximationsignal.

In the step of S50, signal filtering units receive the first detailsignal and the second detail signal from the detecting units. The signalfiltering units generate a first filtering signal by computing the firstdetail signal and the second detail signal in accordance with acorrelation. For example, the signal filtering units generates the firstfiltering signal by multiplying the first detail signal by the seconddetail signal.

In the step of S60, the signal filtering units generate a secondfiltering signal use of a correlation equation. Here, the correlationequation is set to multiply a correlation coefficient, which uses asummed value obtained by squaring a value of the first detail signal anda summed value obtained by squaring a value of the first filteringsignal, by the first filtering signal.

In the step of S70, the signal filtering units compare the first detailsignal with the second filtering signal. Specifically, the signalfiltering units compare an absolute value of the first detail signalwith an absolute value of the second filtering signal to detect a faultdetection signal. If the absolute value of the second filtering signalis greater than the absolute value of the first detail signal, thesignal filtering units determine that the second filtering signal is areflected wave signal reflected by both ends of the cable and detect thesecond filtering signal as a fault detection signal. If the absolutevalue of the second filtering signal is smaller than or equal to thefirst detail signal, the signal filtering units determine that thesecond filtering signal is a noise and remove the second filteringsignal. Then, the signal filtering units detect the first detail signalas the fault detection signal. The fault detection signal is a signalthat allows detection of time at which a fault signal is reflected in amain line of the cable after the fault signal travels to either end ofthe main line when a fault occurs. The signal filtering units output thefault detection signal to a computing unit.

In the step of S80, the computing unit detects the fault detectionsignal at either end of the cable. Then, the computing unit computes adelay time of the detected fault detection signal by use of a datacommunication device. Then, the computing unit computes the distance tothe location of fault by using the delay time of the fault detectionsignal and a transmission speed of the cable.

The method of detecting a location of fault in a cable in accordancewith an embodiment of the present invention makes an on-line detectionof the location of fault by using a progressive wave and computes thelocation of fault by using the fault signal detected in the main line ateither end of the cable. Since it only requires that the first signalarriving in the main line at either end of the cable is detected, themethod of detecting a location of fault in a cable in accordance with anembodiment of the present invention is not affected by the reductionoccurred in later-arriving signals. Therefore, unlike an off-line methodof detection a location of fault, the on-line detection of the locationof fault can be made as soon as the fault occurs, enabling a rapiddetection of the fault location and minimizing the time and costrequired for repair.

The embodiment of the present invention can include a computer-readablemedium that includes program commands for executing operations realizedin various computers. The computer-readable medium can include programcommands, local data files and local data structures individually or incombination. The medium can be specially designed and constructed forthe present invention or can be known and usable by anyone skilled incomputer software.

Hitherto, the present invention has been described with reference tosome embodiment. There can be many other embodiments in addition to thedescribed embodiment within the claims of the present invention. Itshall be understood by a person of ordinary skill in the art to whichthe present invention pertains that the present invention can beembodied in modified forms without departing from the essential featuresof the present invention. Therefore, the disclosed embodiment shall beunderstood in a descriptive perspective, not a restrictive perspective.The scope of the present invention is disclosed in the appended claims,not in the above description, and it shall be interpreted that alldifferences within the equivalent scope are included in the presentinvention.

1. A system for detecting a location of fault in a cable, the systemcomprising: a cable, transmitting a fault current; a currenttransforming unit, connected to the cable and receiving the faultcurrent and detecting an original signal of fault current; a detectingunit, detecting a first detail signal and a second detail signal fromthe original signal of fault current, the first detail signal and seconddetail signal being detail components in a high frequency band; acomparing unit, comparing the first detail signal with a presetreference value and determining a fault in the cable; and a signalfiltering unit, generating a first filtering signal and a secondfiltering signal by use of the first detail signal and the second detailsignal and outputting a fault detection signal based on a result ofcomparing the first detail signal with the second filtering signal. 2.The system of claim 1, wherein the detecting unit detects a firstapproximation signal and the first detail signal by applying wavelettransform to the original signal of fault current, and detects a secondapproximation signal and the second detail signal by applying wavelettransform to the first approximation signal.
 3. The system of claim 2,wherein the detecting unit detects the second detail signal if the firstdetail signal exceeds the reference value.
 4. The system of claim 1,wherein the filtering unit generates the first filtering signal bymultiplying the first detail signal by the second detail signal.
 5. Thesystem of claim 1, wherein the signal filtering unit generates thesecond filtering signal by use of a correlation equation of the firstdetail signal and the first filtering signal.
 6. The system of claim 5,wherein the correlation equation is set to be${{C\_ new} = {C \times \sqrt{\frac{\sum D_{1}^{2}}{\sum C^{2}} \times 2}}},$C_new being a second filtering signal, C being a first filtering signal,D₁ being a first detail signal.
 7. The system of claim 1, wherein thesignal filtering unit outputs the fault detection signal by comparing anabsolute value of the second filtering signal with an absolute value ofthe first detail signal, whereas the fault detection signal is outputtedwhen the absolute value of the second filtering signal is greater thanthe absolute value of the first detail signal.
 8. The system of claim 7,the signal filtering unit removes the second filtering signal when theabsolute value of the second filtering signal is smaller than theabsolute value of the first detail signal.
 9. The system of claim 1,further comprising a computing unit, the computing unit receiving thefault detection signal from the signal filtering unit and computing adistance to the location of fault by using a delay time of the faultdetection signal and a transmission speed of the cable.
 10. The systemof claim 9, further comprising a communication device, the communicationdevice being connected to the signal filtering unit and the computingunit and providing the delay time of the fault detection signal to thecomputing unit.
 11. A method of detecting a location of fault in acable, the method comprising: extracting an original signal of faultcurrent at either end of a cable; detecting a first approximation signaland a first detail signal from the original signal of fault currentthrough wavelet transform; determining whether or not a fault isoccurred in the cable by comparing the first detail signal with a presetreference value; detecting a second approximation signal and a seconddetail signal from the first approximation signal through wavelettransform; generating a first filtering signal by computing the firstdetail signal and the second detail signal; generating a secondfiltering signal with a correlation equation that is set by using thefirst detail signal and the first filtering signal; and outputting afault detection signal by comparing the first detail signal with thesecond filtering signal.
 12. The method of claim 11, the second detailsignal is detected when the first detail signal exceeds the referencevalue.
 13. The method of claim 11, wherein, in the step of determiningwhether or not a fault is occurred in the cable, the cable is determinedto be in a normal state if the detail signal is below or equal to thereference value.
 14. The method of claim 11, wherein the first filteringsignal is generated by multiplying the first detail signal by the seconddetail signal.
 15. The method of claim 11, wherein, in the step ofoutputting the fault detection signal, an absolute value of the firstdetail signal and an absolute value of the second filtering signal arecompared.
 16. The method of claim 11, further comprising detecting alocation of fault in the cable by using the fault detection signal. 17.The method of claim 16, wherein the location of fault in the cable iscalculated using a delay time of the fault detection signal and atransmission speed of the cable.
 18. The method of claim 11, wherein thecorrelation equation is set to be${{C\_ new} = {C \times \sqrt{\frac{\sum D_{1}^{2}}{\sum C^{2}} \times 2}}},$C_new being a second filtering signal, C being a first filtering signal,D₁ being a first detail signal.
 19. The method of claim 11, wherein thefault detection signal is detected if an absolute value of the secondfiltering signal is greater than an absolute value of the first detailsignal by comparing the absolute value of the second filtering signalwith the absolute value of the first detail signal.
 20. A recordingmedium having recorded a program for realizing a method of detecting alocation of fault in a cable of a power transmission system, therecording medium being readable by an electronic device, the methodcomprising: extracting an original signal of fault current at either endof a cable; detecting a first approximation signal and a first detailsignal from the original signal of fault current through wavelettransform; determining whether or not a fault is occurred in the cableby comparing the first detail signal with a preset reference value;detecting a second approximation signal and a second detail signal fromthe first approximation signal through wavelet transform; generating afirst filtering signal by computing the first detail signal and thesecond detail signal; generating a second filtering signal with acorrelation equation that is set by using the first detail signal andthe first filtering signal; and outputting a fault detection signal bycomparing the first detail signal with the second filtering signal.